Health & Wellbeing

Asthma rates double from inner cities to outer suburbs. Here's why

Asthma rates double from inner cities to outer suburbs. Here's why
A study found stark differences in asthma risk when comparing inner and outer cities
A study found stark differences in asthma risk when comparing inner and outer cities
View 1 Image
A study found stark differences in asthma risk when comparing inner and outer cities
A study found stark differences in asthma risk when comparing inner and outer cities

Combining census data with cutting-edge statistical analysis and satellite imagery, researchers have revealed a stark difference between inner- and outer-city living in terms of the risk children have of developing asthma.

It seems logical that the increased traffic fumes and other air pollution associated with living in the inner city would increase asthma risk in children compared with living in the outer suburbs. However, according to a new Australian study, the reverse is true.

The study, led by researchers from the Telethon Kids Institute and Curtin University, combined 2021 census data with cutting-edge statistical modeling and satellite imagery to map the distribution of childhood asthma. What they found was a stark gap between inner and outer city living.

“We took the data for the four largest cities – Sydney, Melbourne, Brisbane and Perth – and focused on asthma to try and figure out what risk factors could predict spatial patterns of occurrence in children aged 5–14 years,” said Ewan Cameron, an expert in geospatial modeling and the study’s lead author.

The researchers went into the study thinking they’d find what many assume to be the case, that inner-city living increases asthma risk.

“Going in, we thought the inner city might have the most childhood asthma because of heavy traffic flow and air pollution, but instead, the pattern we see is one of increasing asthma risk towards the outer areas of cities,” Cameron said. “The suburbs, with 12 percent prevalence, had twice the rate of childhood asthma as the inner city (6%).”

Cameron attributes this geographical disparity to a combination of socioeconomic factors and combined climate and environmental factors that are almost equally split in terms of their respective contributions. Climatic and environmental factors contributed 30%, outdoor air pollution 19%, and socioeconomic status the remaining 51%.

“In many ways, it was surprising just how similar all the cities were,” he said. “We found that in every city, there was that same trend – increasing prevalence from the wealthier inner-city suburbs to the poorer outer-city suburbs. We know from earlier studies … that the risk of developing asthma is strongly shaped by socioeconomic factors. These factors include higher rates of chronic family stress and poor housing quality, including dampness and poorly ventilated gas stoves, as well as dietary and obesity factors. People in lower socioeconomic areas, many of whom are renting, often lack the means to alleviate these issues and may have poorer access to healthcare support for asthma management.”

Using satellite imagery to ascertain the levels of pollutants around each city, along with vegetation, temperature and rainfall variations, the researchers saw the significant role climate and environmental factors played.

“We do find there’s a contribution from environment – places that experience large daily temperature variations tend to have [a] higher risk of asthma,” said Cameron. “More extreme weather can be a factor in triggering asthma.”

According to the World Health Organization, asthma is the most common chronic disease among children globally. Studies like the current one highlight the challenges faced by health authorities and governments when trying to manage the condition.

“By revealing where asthma risk is highest at a fine level of precision – down to neighborhood block size – we can identify the local government areas that need the most support,” Cameron said.

The 2021 census was the first to include a question about long-term health conditions. The researchers are looking forward to analyzing the data collected in the next census in 2026 and comparing the two.

“We’re excited about getting the results from the next round – this will give us a new time point to mark any changes in chronic disease prevalence and, in combination with insights from other key surveys and datasets, help us to strengthen the evidence around spatial health inequalities in Australia’s major cities,” said Cameron.

The study was published in the Journal of Allergy and Clinical Immunology.

Source: Telethon Kids Institute

Of course this is the case and there are some clear culprits. The most obvious being leaf blowers. With the advent of leaf blowers (these are suburban necessities, apparently), the air quality and particulate counts increased dramatically.
People are VERY difficult to study. And while the paper's authors speculate about certain differences that trigger asthma, this study can't really show that.

One reason this study doesn't prove anything is that inner city and suburb populations are different in several ways;

- At least in the U.S., there are significant racial differences.
- Family differences, with more out-of-wedlock children in cities. So inner city kids have a less stable home life.
- Rates of drug abuse differ.
- Mental health differs, since those with mental problems are less likely to have a higher income.
- The article mentions less access to healthcare, but it is also possible that more access to healthcare could be a trigger.
- The hygiene hypotheses for autoimmune diseases has been pretty well established in mouse models. Turns out having a pet, and things like eating some dirt while playing outside as a young child is beneficial to train the immune system to behave properly. Such things vary with the community.

The article mentions that some of these can be adjusted for in the study cited in the article. Well, at least adjusted to some extent. But, in the end, such studies can only bring up some ideas to test in a lab. The study itself can't prove anything.
Hygiene hypothesis:
In medicine, the hygiene hypothesis states that early childhood exposure to particular microorganisms (such as the gut flora and helminth parasites) protects against allergies by strengthening the immune system.[1][2] In particular, a lack of such exposure is thought to lead to poor immune tolerance.[1] The time period for exposure begins before birth and ends at school age.